The invention is based on a hydraulic braking system, especially for motor vehicles, having a device for anti-lock control and for generating a differential lock by brake engagement, as defined hereinafter.
A hydraulic braking system has already been proposed (DE-A1-40 34 112), in which both an anti-lock control mode and a traction control or drive slip control mode are possible in a brake circuit associated with the two driven wheels of the vehicle. To that end, the control unit switches the appropriate elements of the braking system in accordance with a predetermined control algorithm. To simultaneously limit drive slip at both driven wheels, it is necessary to equip the braking system with one outlet valve for each of the corresponding wheel brakes and to embody the control unit appropriately. Automobile manufacturers, however, also demand braking systems that for slip limitation allow a braking engagement limited to one driven wheel.
From DE-C1 40 09 640, FIG. 3, a hydraulic braking system is known, in which in all phases of the brake pressure modulation in traction control, the high-pressure pump aspirated pressure fluid via the charging valve switched into its open position and feeds it into the brake line, which is blocked off from the master cylinder by the blocking valve. Pressure fluid not drawn from the wheel brake of the vehicle wheel suffering the drive slip must therefore be diverted from the brake line to the suction line via a pressure limiting valve. Moreover, in the phase for pressure reduction, the outlet valve associated with the affected wheel brake is used for pressure relief.
A traction control apparatus of a hydraulic braking system is also known from DE-C1-39 00 851, in which in the phase for brake pressure buildup a high-pressure pump aspirates pressure fluid from a master cylinder, via a charging valve switched into the open position, and feeds it into a brake line leading to wheel brakes, the brake line being monitored toward the master cylinder by a blocking valve. The feeding of pressure into the wheel brake subjected to the drive slip is done by means of an associated inlet valve of a valve assembly for brake pressure modulation, whose outlet valve remains in its blocking position in all the phases of pressure modulation in traction control. The pressure reduction in the wheel brake is controlled by means of the inlet valve and the blocking valve. The triggering of the high-pressure pump and of the charging valve in the phases for pressure holding and pressure reduction, and of the blocking valve in the first of these phases, is not disclosed.